The present invention relates to a helicopter or rotary wing aircraft rotor structure, wherein the wings or blades are arranged in pairs and the members of a pair are located diametrically opposite each other. The wings or blades are secured to the rotor head without flapping hinges and without drag or lagging hinges, however, not in a rigid manner. There are provided blade angle bearings which secure the blades or wings to the rotor head radially outwards thereon. The blade angle bearings permit the movement of the blades through an pitch angle range and support the blades in a rotatable manner. Two blades forming a pair are interconnected respectively at the blade or wing roots by means of a tension bar element which is elastic against torsion loads between its ends.
German Pat. No. 1,531,355 discloses a rotor of this type including a rigidly constructed rotor head. The rotor blades or wings are rotatably secured to the rotor head. One end of each rotor blade is rigidly supported and two rotor blades are interconnected as a pair by means of laminated bars rigid against tension but elastic relative to torsion and bending loads. In such a structure the bending moments effective at the blade or wing roots must be taken up by the blade angle bearings and by the rotor head, whereby these stuctural elements are subject to substantial loads requiring a respectively strong dimensioning which in turn results in a correspondingly high structural weight. Further rotor systems are well known in the art in which the rotor head itself is constructed to be flexible, thereby taking up the major proportion of the deformations occurring when the blades or wings perform a flapping motion. This type of structure, however, results in a disadvantageous position of the fictitious or assumed flapping hinges radially inside the blade angle bearings, whereby the control characteristics of the rotor are influenced in a disadvantageous manner. Besides, this type of structure results in substantial bending moment loads to which the rotor head is subjected, whereby the moment curve or characteristic rises steeply toward the rotor axis. Further, large shearing loads or stresses occur in the area where the largest deformations take place so that the rotor head must be constructed on the one hand to easily yield against bending in the flapping direction and on the other hand, it must be capable of withstanding high dynamic loads. These two requirements are incompatible with each other and hence it is difficult to realize such a structure in practice unless a high expense and a heavy structural weight are not avoided in order to assure a safe function or operation.
German Patent Publication (DOS) No. 2,452,535 discloses an arrangement in which the rotor blades are interconnected in pairs by means of a carrier spar or beam which is yielding against bending and elastic against torsional loads. The carrier beam is secured to a rigidly constructed rotor head adjacent to the rotational axis of the rotor by means of closely spaced, angularly movable and axially displaceable bearing points which secure the carrier beam in a manner rigid against rotation. Such a structure, however, also has large peaks in the bending moment curve, especially adjacent to the rotational axis of the rotor. In addition, the structure is generally subject to rather undesirable flapping motions of the rotor blades or wings.